The invention relates to coating structures that are resistive to corrosive attack in an environment of chlorine and metal chloride(s), such as NaCl, LiCl, KCl, AlCl.sub.3, MgCl.sub.2, TiCl.sub.4, FeCl.sub.3 and SiCl.sub.4.
As discussed in U.S. Pat. Nos. 3,745,106; 3,745,107; 3,809,974 and 3,838,384, all to Stanley C. Jacobs, the commercial realization of the advantages of utilizing aluminum chloride as a source material in the electrolytic production of aluminum has been hampered by the presence of certain unresolved problems, not the least of which has been the provision of low electrical resistance electrode assemblies for applying and removing current to and from the cells employed in the reduction process, and in the process of making aluminum chloride from chlorine gas, alumina-bearing material and carbon in a furnace chamber electrically heated by graphite-resistant heaters. This latter process is discussed, for example, in U.S. Pat. No. 4,171,346 to King et al. The present invention, however, is not limited to the making of aluminum and aluminum chloride. Rather, the invention encompasses the protection of a metal substrate in any metal chloride or chlorine environment at temperatures particularly in a range of 100.degree. to 650.degree. C., such an environment being highly corrosive of all known metals exposed to such an environment.
The efficiency and economy of operation that necessarily attend commercial furnace and cell performance dictate the utilization of low electrical resistance, high current-carrying conductor members wherever possible. Any rapid deterioration of the conductor material, as caused by the above corrosive environment, can only result in markedly reduced performance, and also in frequent shutdown and undue repair and maintenance time and expense, all of which are antithetical to the operational requisites for continuous commercial quantity in the production of metal and the metal chloride.